1. What is Prismatic Coefficient?

Definition: The prismatic coefficient (Cp) is a dimensionless value that represents the ratio of the displaced volume of a ship's hull to the volume of a prism with length equal to the ship's length and cross-sectional area equal to the midship section area.

Purpose: It's a key parameter in naval architecture that indicates the fineness of a ship's hull form and affects resistance and propulsion efficiency.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( C_p \) — Prismatic coefficient (dimensionless)
• \( V \) — Displaced volume (m³)
• \( A_m \) — Midship section area (m²)
• \( L \) — Length (m)

Explanation: The ratio compares the actual underwater volume of the hull to the volume of a prism with constant cross-section equal to the midship section.

3. Importance of Prismatic Coefficient

Details: Lower Cp values indicate finer hulls with better performance at higher speeds, while higher Cp values indicate fuller hulls better suited for slow-speed, high-capacity vessels.

4. Using the Calculator

Tips: Enter the displaced volume in cubic meters, midship section area in square meters, and length in meters. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical range for prismatic coefficient?
A: For most ships, Cp ranges between 0.55 (fine hulls) to 0.85 (full hulls). High-speed vessels may be as low as 0.50.

Q2: How does prismatic coefficient affect ship performance?
A: Lower Cp generally means less resistance at higher speeds but reduced cargo capacity. Higher Cp means more capacity but higher resistance at speed.

Q3: Where can I find the midship section area?
A: This is typically available in the ship's lines plan or hydrostatic calculations. It's the submerged cross-sectional area at the midship section.

Q4: Is prismatic coefficient the same as block coefficient?
A: No, block coefficient (Cb) compares volume to a rectangular block, while prismatic coefficient compares to a prism with midship section shape.

Q5: How is displaced volume calculated?
A: Displaced volume can be calculated from hydrostatic tables, CAD models, or by dividing displacement (mass) by water density (typically 1.025 t/m³ for seawater).